This application claims the priority of German Application No. 100 18 739.0 filed Apr. 15, 2000, which is incorporated herein by reference.
An electromagnetic actuator for operating a cylinder valve of a piston-type internal-combustion engine has to be mass produced in large numbers in an economical manner. Such an electromagnetic actuator includes opening and closing electromagnets having spaced, facing pole faces, an armature reciprocated between the pole faces and coupled to the cylinder valve to move the latter into open and closed positions, as well as opening and closing (resetting) springs opposing the armature motion.
German Offenlegungsschrift (application published without examination) 198 25 728 discloses an electromagnetic actuator of the above-outlined type. The electromagnets are each provided with a respective, separate housing for receiving the magnet yoke which supports a coil. Such housings make possible a mass produced assembly of complete electromagnetic actuators. The housings are expediently made of a non-magnetic metal, for example, aluminum or an aluminum alloy so that they may be mass produced with a suitable casting process (such as die casting) in large numbers in an economical manner and adapted to individual requirements. On its side oriented away from the pole face of the inserted yoke body, the housing is provided with a tubular passage for receiving one end of a resetting spring. Thus, each housing may be used either for the part serving the opening function or the part serving the closing function.
In the housing oriented towards the cylinder valve the closing spring extends through the housing passage and is supported at its ends by the engine block and, respectively, by a spring seat disk affixed to the cylinder valve stem.
In the housing oriented away from the cylinder valve the opening spring passes through the housing passage and is supported on a threaded sleeve, by means of which the mid position of the armature between the pole faces of the two electromagnets may be adjusted. Such a threaded sleeve involves not only high manufacturing and assembly costs but also has disadvantages as concerns the reproducibility of an optimal setting and its handling during maintenance work.
It is an object of the invention to provide an improved electromagnetic actuator of the above-outlined type from which the discussed disadvantages are eliminated.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the electromagnetic actuator for operating a cylinder valve in an internal combustion engine includes first and second housings secured to one another. Each housing has a cavity and a through bore extending therefrom. First and second electromagnets are disposed in the cavity of the respective housings. Each electromagnet has a yoke, a coil and a pole face. The pole faces are oriented toward and spaced from one another, and a reciprocating armature is disposed between the pole faces. A spring which urges the armature away from the first electromagnet has an end oriented away from the armature. A support cap is axially insertable in the through bore of the first electromagnet and includes a cap base having an inner face supporting the spring end. A locking arrangement secures the support cap to the housing and has a component axially insertable in the through bore with the support cap.
By eliminating the conventional, disadvantageous threaded sleeve, both actuator housings may be made from identical blanks without major finishing costs. By using an axially insertable support cap including a plug-in lock, cutting threads into the housing for a threaded adjusting sleeve cooperating with the opening spring is no longer needed. Merely geometrical elements for a plug-in lock are needed which may be readily formed in the housing blank. The presence of such housing configuration is harmless for the other, cap-less housing (accommodating the opening magnet) because, as concerns the opening magnet, only the closing spring is received in the housing passage and therefore any particular housing shape required for the support cap does not cause disturbance during service. Plug-in support bodies may be installed in a simple manner and further have the advantage that they may be made in large numbers of shaped steel sheet. Making the support cap from steel sheet also has the advantage that the cap, although exposed to high tension forces, may be relatively thin-walled. A further advantage compared to a conventional thread provided in the actuator housing resides in the fact that the securing and locking means can be made as large-area members so that the securing means of the steel supporting cap and the housing (such as an aluminum casting) may engage one another with a low surface pressure.
According to a preferred embodiment of the invention, in the region of the through bore the support cap and the housing together form the support cap lock which immobilizes the support cap in the actuator housing. This is achieved by configuring the lock as a bayonet lock composed of at least one radial projection and a receiving element for accommodating the projection, provided, for example, on the outer surface of the support cap and the housing, respectively. Upon assembly, the support cap may be plugged into the housing passage (through bore) and is thereafter rotated about its axis to lock it in place.
According to a particularly advantageous feature of the invention the projection and/or the projection receiving element is configured as a helical ramp in relation to the longitudinal actuator axis. As a result, by rotating the support cap relative to the housing, the bias of the opening spring may be changed and thus the mid position of the armature between the two pole faces may be adjusted. According to the invention, securing means are provided for fixing the support cap in the housing in a predeterminable position of installation.
According to a further advantageous feature of the invention, the outer surface of the cap base whose inner bottom surface is engaged by the opening spring is provided with at least one element for receiving a mounting tool. Such an element may be a rectangular opening provided in the cap base or two openings radially spaced from the central axis of the supporting cap to receive, respectively, a quadrilateral wrench or a hook wrench. After inserting the supporting cap into the housing bore while compressing the opening spring, the support cap may be turned into its locked position by the wrench inserted into the receiving element.
In accordance with a further advantageous feature of the invention, at least the base of the support cap made of steel sheet is tempered (hardened). The opening spring engages at one end a spring seat disk which is made of a wear resistant material and which is affixed to an armature guide bar. The other end of the opening spring engages the inner surface of the cap base. Since at that location substantial spring forces have to be taken up and the support of the springs in operation is exposed to a fluctuating pressing load, a hardened cap base prevents the spring end from working itself into the cap material.
Instead of providing a helical ramp for the projection and/or the projection-receiving element of the bayonet lock for the support cap, according to another feature of the invention at least one adjusting washer is positioned on the inner face of the cap base for engaging the opening spring. By inserting adjusting washers of different thicknesses or as a stack, it is possible to adjust, within the required accuracy, the mid position of the armature between the two pole faces. By virtue of this measure the structure of the lock between the support cap and the housing is simplified since the support cap needs only to be inserted into the housing bore and then locked to the housing by rotation.